The use of intraocular lenses ("IOLs") has been highly developed in recent years, especially for implantation after the removal of a cataract, and such operations are now common medical procedures. In such procedures it is desirable to minimize the size of the incision which must be made to insert and position the IOL in the eye, in order to shorten the time required for the eye to heal and to minimize any chance of failure. Most implanting techniques have required that the incision in the eye be slightly wider than the diameter of the IOL to be implanted so that the lens can be inserted through the incision. Recently techniques have been developed for reducing the width of a lens by folding it prior to insertion. The use of a folded lens enables a smaller incision to be used than otherwise would be required. For example, a lens of 6.0 mm diameter can, if folded, be inserted through an incision only about 3.2 mm wide.
My U.S. Pat. No. 4,769,034 discloses a foldable resilient lens which is retained in a folded configuration, by a retainer which is wrapped around the lens and temporarily held in place by severable ties around the folded lens. This enables the lens to be inserted through the same small incision which is used to remove a cataract from the eye. Once inserted in the eye the retainer is released and removed, and the lens resiliently unfolds to its normal configuration. My U.S. Pat. No. 4,911,914 discloses another type of retainer for holding a lens folded during insertion, in which the retainer is integral with the lens itself. Sutures which extend through apertures in overlying parts of the folded lens are also disclosed.
My U.S. Pat. No. 4,819,631 discloses apparatus for folding a lens for insertion. That apparatus presents a lens seat on which the lens is placed. A base has a guide for aligning an inserter so that the blade of the inserter is properly positioned on the lens. A hinged or swingable folding arm folds one half of the lens around the blade. Preferably the inserter blade has a teardrop-shaped cross section which closely conforms to the space between the leaves of the folded lens so that the lens surface closely engages the blade.
The techniques referred to above are relatively complicated in that they require securing a retainer around or suturing the folded lens, or forming a retainer integrally with the lens. My U.S. Pat. No. 4,988,352 discloses an intraocular lens which is retained in the folded configuration by chilling it until it becomes inflexible and looses its tendency to unfold. A cryogenic gas is applied to rigidify the lens. The chilling (which can be thought of as "freezing" even though no liquid/solid phase change occurs) obviates the need for a surrounding or attached retaining means to hold the lens in the folded configuration. This facilitates the surgical procedure and enables a smaller incision to be used. The rigidified folded lens is inserted into the eye and there warms so that it returns to its original flexible, unfolded configuration. The lens may be rigidified on an inserter or blade for positioning it within the eye.